Repurposing Chemotherapeutics in a Hyaluronic Acid-conjugate Combination Treatment Approach for the Local Immunomodulation of the Glioblastoma Microenvironment

The immunosuppressive tumor immune microenvironment (TIME) renders glioblastoma (GBM) refractory to current chemo-immunotherapeutics. We sought to explore a novel approach for local GBM-associated TIME immunomodulation based on a synergistic combination of the repurposed chemotherapeutic drugs doxorubicin (DOX), which acts to induce immunogenic cell death (ICD) and gemcitabine (GEM), which depletes immunosuppressive myeloid-derived suppressor cells (MDSCs). We conjugated DOX and GEM to hyaluronic acid (HA) to improve efficacy, given this polymer's ability to target CD44 which are overexpressed on cancer cells. The HA-DOX and HA-GEM polymer-drug conjugates provided synergistic cytotoxic effects and maintained ICD-related properties in GBM cells compared to a combination of free drugs. HA-DOX and HA-GEM also reverted the immunosuppressive GBM-associated TIME in orthotopic GL261 tumor-bearing mice by selectively depleting MDSCs and reprogramming M2-like macrophages towards a pro-inflammatory M1-like state, resulting in controlled tumor growth. Local HA-DOX and HA-GEM delivery also increased median survival and controlled tumor growth in an immune refractory SB28-GBM orthotopic mouse GBM model. These findings highlight the potential of repurposing clinically applicable chemotherapeutics in the context of polymer-drug combination treatments for novel immunomodulation strategies in unresectable GBM, which may open new avenues for developing innovative therapies.